The present invention relates to a process for manufacturing a high frequency multichip module that includes a high frequency bare chip mounted on a substrate. The bare chip has a ground electrode disposed at the opposite side to the signal electrodes. More particularly, the present invention relates to a process for manufacturing a high frequency multichip module, which can omit a performance test of the small-sized high frequency bare chip after mounting the bare chip and other components on the substrate.
Conventionally, such a bare chip used for manufacturing a high frequency multichip module is mounted on a substrate 1010 as shown in a top view of FIG. 1. On the substrate 1010, signal electrodes 1011 and ground electrodes 1012 are arranged alternately on the same plane. The coplanar type bare chip 1020 also has signal electrodes 1021 and ground electrodes 1022 arranged alternately on the same plane of the coplanar type bare chip 1020, corresponding to the signal electrodes 1011 and ground electrodes 1012. Each of the signal electrodes 1021 and ground electrodes 1022 is connected to the corresponding signal electrode 1011 or ground electrode 1012 by bonding wire 1030.
In order to measure high frequency characteristics of such a coplanar-type bare chip 1020 by a coplanar-type probe 1000, it was a precondition that the signal electrodes 1021 and the ground electrodes 1022 of the coplanar-type bare chip 1020 are arranged on the same plane as illustrated. And the coplanar type probe 1000 has a center conductor tip portion 1001 that is pressed to the signal electrode 1021 and ground conductor tip portions 1002 that are pressed to the ground electrodes 1022. Therefore, the center conductor tip portion 1001 and the ground conductor tip portions 1002 should be arranged on the same plane that is perpendicular to the pressing direction, and as the coplanar-type bare chip 1020.
As illustrated in FIG. 2, a horizontal-type probe or the coplanar-type probe 1110 has conductor tip portions horizontally arranged. The conductor tip portions are a center conductor tip portion 1111 having a flat spring shape and ground conductor tip portions 1112 disposed at the both sides of the center conductor tip portion 1111. And these conductor tip portions 1111 and 1112 are arranged on the same plane. Therefore, the center conductor tip portion 1111 and the ground conductor tip portions 1112 are pressed to the signal electrode 1121 and the ground electrodes 1122 of the coplanar type bare chip 1120 to make electrical contact between each of the conductor tip portions and the corresponding electrode.
As described above, since the coplanar type bare chip 1120 has a signal electrode 1121 and ground electrodes 1122 arranged at both sides of the signal electrode 1121 on the same plane, the area of the coplanar type bare chip 1120 becomes large. For example, if the area of a GaAs-MMIC (monolithic microwave integrated circuit) is large, the number of bare chips that can be made from an expensive GaAs wafer becomes small, so that the cost per chip rises.
When using a peripheral electrode arrangement such as a grid electrode arrangement with bump connection, high cost is still a problem in the same way as described above.
Recently, in order to solve the above-described problem and to obtain a smaller area of the electrodes for external connection capable for high-density mounting, a microstrip-type bare chip is being used. The microstrip-type bare chip has a ground plane on the rear side so as to reduce the ground electrodes on the front side.
However, as illustrated in FIGS. 3A and 3B, using the above-described coplanar type probe 1210, it is difficult to measure the high frequency characteristics of the microstrip-type bare chip 62, because the microstrip-type bare chip 62 has a signal electrode 62-1 only but no ground electrode on the front surface to be contacted with the ground conductor tip portion 1212 of the coplanar type probe 1210. Instead the microstrip-type bare chip 62 has a ground plane 62-2 at the rear side. As the result, the coplanar type probe 1210 does not contact any ground level when the center conductor tip portion 1211 contacts the signal electrode 62-1 on the front surface of the microstrip type bare chip 62.
In order to solve the above-described problem, a quad flat package (QFP) is realized, which has a peripheral electrode arrangement as shown in FIGS. 4A and 4B. In this arrangement, inner electrodes are lead out to the periphery of the chip and arranged flatly. This peripheral electrode arrangement enables measurement with the coplanar-type probe 1312 by arranging the signal electrodes and the ground electrodes alternately on outer-substrate electrodes 1322 via inner-substrate electrodes 1321. On the other hand, measurement with the coplanar-type probe 1311 is not possible since the microstrip type bare chip 1330 mounted on the substrate 1320 has a rear ground plane.
Therefore, as illustrated in FIG. 5, the manufacturing process of the high frequency multichip module illustrated in FIGS. 4A and 4B is realized. At first, a preprocess (step 1401) is performed as a step of component mounting (step 1402) in which the microstrip-type bare chip 1330 and other components are mounted on the substrate 1320, and wire bonding is performed with metal wires 1340. After this step, the coplanar-type probe 1312 is used for the outer-substrate electrodes 1322 so as to measure the high frequency characteristics and to test the performance in a step of a performance test (step 1403). If the mounted component performs well in the performance test ("GOOD" in step 1403), a shipment/manufacture step (step 1404) is performed next in which the product is shipped or the next manufacture step is performed to finish the process (End #1).
If the mounted component is "NG" in the performance test of the above step 1403, it is checked if the mounted component can be replaced with new one in a step of "replaceable" (step 1405). If the replacement is possible by "YES" of step 1405, the mounted component is replaced with a new one in a step of replacing (step 1406) and the process returns to the above-described step 1402 so as to mount and test the performance of the new mounted component.
If the replacement is impossible, in other words, the result of the step 1405 is "NO", this defective product is rejected in the rejection step (step 1407) and the process finishes (End #2).
However, the above-described conventional process for manufacturing the high frequency multichip module has the following problem. Since the conventional probe is coplanar-type, it is difficult to measure the high frequency characteristics of the single bare chip before mounting. Therefore, the performance test of the microstrip-type bare chip should be performed after the mounting of components. In addition, if the result of the performance test is "NG", the defective product should be replaced with a new one. This replacement should be repeated until the result of the performance test is "GOOD", so that the manufacturing time and costs are increased.